Chemical Science. 401 



it has much metallic lustre, is brittle, and of the hardness of fluor 

 spar: spec. gr. = S.I 59. It is mixed with small proportions of 

 tellurium-silver, and before the blowpipe on charcoal, fuses to a 

 small button, which gradually diminishes in size so as ultimately to 

 exhibit a small globule of silver, surrounded by a ring of metallic 

 hue, which seems to be formed by the volatilized and subsequently 

 precipitated tellurium-lead. If the flame is directed upon it, it is com- 

 pletely volatilized, the flame becoming at the same time of a blue 

 colour. It fuses also in a retort, and forms a small quantity of 

 white sublimate, which, under the action of strong heat, contracts 

 into small globules. If ignited in an open tube, it fuses and becomes 

 surrounded by a ring of white drops, and at the lower portion of the 

 tube a very dense white sublimate is deposited, which before the flame 

 of the blowpipe contracts into small drops. 



When powdered, it dissolved in nitric acid with the evolution of red 

 vapours : the solution was diluted with water, and the silver con- 

 tained in it precipitated by muriatic acid ; the fluid was then filtered, 

 and the lead precipitated by hydro-sulphuretted ammonia; after 

 twenty-four hours the fluid was again filtered, the sulphuretted tel- 

 lurium precipitated from it by adding muriatic acid, and the sulphur 

 ultimately separated from the metal by dissolving the sulphuret in 

 nitro-muriatic acid, which precipitated the sulphur. 



As one analysis only could be made of the mineral, M. Rose re- 

 frains from giving any decided opinion on its composition at pre- 

 sent ; he is, however, inclined to consider it as a compound of 1.28 of 

 silver, 60.35 of lead, and 38.37 of tellurium. 



33. BERZELIUS' METHOD OP PREPARING UREA. 



The following process for obtaining urea is recommended by Ber- 

 zelius in his recent work on Chemistry, vol. vi., p. 420, of the 

 Swedish original. 



Recent urine is to be evaporated, and as much of the residuum as 

 possible taken up by alcohol. The alcoholic solution is to be evapo- 

 rated, and the yellow substance remaining, dissolved in a small quan- 

 tity of water, and digested with a little animal charcoal, until it is 

 rendered quite colourless. The liquid is to be filtered, heated to 50 

 Centigr. (122 F.), and as much oxalic acid added as is soluble at that 

 temperature ; on cooling, the oxalate of urea is deposited in colourless 

 crystals. If, instead of 122, the fluid is heated to 212, the solution of 

 oxalic acid becomes of a brown colour and 4 unpleasant smell ; and the 

 crystals, of oxalate of urea, are of a red or reddish-brown colour, but 

 become colourless on adding a small quantity of animal charcoal. 

 On applying gentle heat, so as slowly to evaporate the fluid, the de- 

 position of crystals continues, and their quantity may be further 

 increased by adding a new quantity of oxalic acid as soon as the 

 fluid becomes thick and loses its sour taste. After this process, all the 

 crystals are collected, washed with ice-cold water, and then again dis-* 

 solved in boib'ng water with a little animal charcoal ; when filtered 



